OLED (Organic Light-Emitting Device) is a kind of light-emitting device using an organic solid semiconductor as a light-emitting material. Since it has the advantages such as simple process of preparation, low costs, low energy consumption, high luminosity, broad working temperature, etc., it has broad perspective of application.
As shown in FIG. 1, the structure of an existing OLED usually comprises a substrate 1, an anode layer 2, a cathode layer 10, and an organic functional layer disposed between the anode layer 2 and the cathode layer 10, the organic functional layer comprising, in sequence, a hole injection layer 3, a hole transport layer 4, an electron blocking layer 5, a light-emitting layer 6, a hole and exciton blocking layer 7, an electron transport layer 8, and an electron injection layer 9. The hole injection layer 3 is adjacent to the anode layer 2, and the electron injection layer 9 is adjacent to the cathode layer 10.
The light-emitting mechanism of an OLED is as follows: when a voltage is applied across the anode layer 2 and the cathode layer 10, driven by the external voltage, the holes injected from the anode layer 2 enter the light-emitting layer 6 through the hole injection layer 3 and the hole transport layer 4, the electrons injected from the cathode layer 10 enter the light-emitting layer 6 through the electron injection layer 9 and the electron transport layer 8; the holes and the electrons entering the light emitting layer 6 recombine with each other in the recombination region to form excitons, which undergo radiative transition to emit light, that is, resulting in electroluminescence.
Since the holes and the electrons have different mobility, the recombination region usually is located within the light-emitting layer and close to the interface with the electron transport layer. After the formation, the excitons diffuse towards both sides of this interface. Some excitons may diffuse to regions undoped with a light-emitting material and decay there, thereby resulting in non-radiative transition.
To sufficiently utilize the energy released from the recombination of the electron and hole carriers, improve the carrier utilization ratio in an OLED, and thus to improve the efficiency of light-emitting of the OLED is an issue in urgent need to be solved in the organic electroluminescence field.